This invention relates to reciprocating pumping units, and more particularly, a pumping unit having variable output without using a transmission between the pump and the prime mover therefor.
Reciprocating pumping units are well known, and such units have been used extensively in oil field applications, such as for pumping water into and out of the wells. Reciprocating pumps are known as fixed or positive displacement pumps.
Prime mover power sources for these pumps are typically diesel engines, but other devices may be used. Multi-ratio automatic transmissions are typically used to drive the pumps to achieve a finite selection of flow rates or pumping rates. Minor flow rate “rangeability” is enabled within any given gear in the transmission by varying the engine speed, but this often requires the engine to operate at less than its maximum horsepower capability which is obviously inefficient. Further, such pumping unit configurations cannot begin pumping at full engine speed, because they are not capable of withstanding the sudden stress on engaging the transmission at full engine speed. Instead, the transmission is shifted into the selected gear while the engine is at low speed, and the pump is at rest. The gear range is selected based on the desired initial pump discharge rate. After engaging the transmission, the engine speed is increased, thus transferring power through the torque converter in the transmission. Only then can the engine speed be increased to the engine's maximum horsepower rating. Once pumping has thus commenced, the transmissions may be shifted “on-the-fly” to achieve various discharge flow rates in an attempt to keep the engine operating near its peak power speed.
Such pumping unit designs do not provide infinitely variable discharge rates at full horsepower, and there is a need for a pumping unit which does provide this feature. A further problem with the prior art pumping units is that, as power requirements increase, the reliability of existing transmissions has proven to decrease to an unacceptable level.
The present invention solves these problems by providing a variable displacement pumping machine consisting of a multiple-crankshaft pump driven by a rotational power source which is enabled to operate at a constant speed if desired and thus take full advantage of the full power of the power source at any given discharge flow rate.